The preparation and the optical properties of lanthanum fluoride (LaF3) nanoparticles doped with erbium and neodymium will be discussed. Organic and inorganic materials in the form of polymers and sol-gels were used to serve as the hosts for the inorganic nanoparticles, respectively. The organic host material has been synthesized such that it is photo-crosslinkable to facilitate straightforward multimode and monomode waveguide fabrication. Our focus will be on the optical properties of both the inorganic rare-earth doped nanoparticles and the host materials. The importance of the refractive indices of the particles and the host material and particle size on the optical scattering properties will be addressed. The optical transmission windows of the host materials do overlap with the absorption peaks of the erbium and neodymium in order to have efficient optical pumping, as well as with the spontaneous emission spectra of the rare earth metals for use as optical amplifiers around 1330nm and 1550nm. Furthermore, the improvement on the excited state lifetimes of the rare earths in the nanoparticles compared to the lifetimes of rare earths directly immersed in sol-gels will be presented.